(1) Field of the Invention
This invention relates to a switching apparatus, communication apparatus, and communication system and, more particularly, to a switching apparatus for routing a packet, communication apparatus for performing multicast communication, and communication system for accommodating many lines and controlling communication.
(2) Description of the Related Art
With the rapid spread of the Internet, there has been a sharp increase in demand for efficient large-capacity IP (internet protocol) traffic in recent years. Therefore, it is hoped that a high-speed large-capacity routing apparatus will be realized.
If multicast communication, for example, is performed, a routing apparatus will copy a packet when it selects a transfer route to a destination address on a network.
With a conventional technique for copying a packet, a received packet is temporarily stored in a buffer at first. Then a routing table prepared in advance is searched for an output route with an identifier in the packet as a key. And then reading from the buffer is performed according to output route information obtained. As a result, one packet is sent to a plurality of output routes.
However, a routing apparatus which uses the conventional technique for copying a packet described above will need to accommodate a huge number of lines when it handles large-capacity traffic at high speed, resulting in a huge number of queues used according to packet types and output routes and in a large-scale routing table.
On the other hand, routing an IP frame will need not packet-by-packet processing but frame-conscious processing because a variable-length frame is input.
In other words, with packet-by-packet processing on an ATM fixed-length packet (cell), reversion of the order of sending may occur at the time of routing because a destination address for a cell is specified from the very first. Cells can be treated independently of one another.
With IP traffic, however, when a variable-length frame is divided into fixed-length packets and routed, the order of the packets at the time of the division must be guaranteed. Packets therefore cannot be treated independently of one another.
As described above, when a process, such as a multicast, is performed on IP traffic, a variable-length frame is divided into fixed-length packets in an apparatus. Therefore, the continuity of packets at the time of generating a frame must be guaranteed at the time of writing to and reading from a buffer. Furthermore, the conventional technique will make address management in a buffer extremely complicated if multicast communication, for example, is also taken into consideration. This will interfere with high-speed processing.